Summary
Gelfiltrations on Sephadex G-25 revealed three different fractions of dissolved labelled P compounds: orthophosphate, and two corresponding to the fractions, which Lean (1973a, b) called colloidal-P (a high molecular weight compound, MW > 5 · 106) and XP (of smaller size, MW ∼ 250). Colloidal-P and XP were not utilized as P sources by microorganisms and they resisted attack from enzymes capable of breaking down the most common biological P compounds.